Vastly improved SQL exporter
- Added lazy_constraints parameter to constructor to control where to put table constraints (after inserts by default for better import performance on databases )
- Added escape_char parameter to constructor to control what escaped character use to quote values
- Moved table indexes to be added after inserts
- Updated output comments
- Changed output indentation from 4 to 2 spaces
- Fixed broken SQL.__quote() signature
- Tweaked SQL.__quote() to not do unwanted conversions and use SQL._escape_char as escape char
- Added SQL.__constraints() helper
- Tweaked SQL.__primaryKey() and SQL.__foreignKey() helpers for lazy_constraints
- Simplified SQL.__primaryKey() and SQL.__foreignKey() helpers signatures
- Added SQL._constraints container
- Tweaked SQL.__indexes() helper line breaking
- Improved containers unpacking
- (Bonus) Updated SQLite3 exporter to use the new SQL constructor arguments